1. Field of the Invention
The present invention relates generally to a variable displacement type refrigerant compressor. More particularly, the present invention relates to a variable displacement refrigerant compressor accommodating therein a novel displacement control valve, which can be easily and accurately assembled in a compressor housing and can be an inexpensive mechanical element. The present invention further relates to a method of assembling the novel displacement control valve in the compressor housing.
2. Description of the Related Art
U.S. Pat. No. 4,688,997 discloses a typical variable displacement type refrigerant compressor adapted to be incorporated in a vehicle climate control system. The variable refrigerant compressor has a compressor housing in which a suction chamber, a discharge chamber, a crank chamber, a reciprocating piston mechanism to compress a refrigerant in a cylinder bore, a piston actuating mechanism including a cam plate mounted around a drive shaft to convert the rotation of the drive shaft in the reciprocation of the piston mechanism, and a displacement control valve unit, are mounted.
The displacement control valve unit of the refrigerant compressor of U.S. Pat. No. 4,688,997 includes a fluid supply passage extending from the discharge chamber to the crank chamber to supply a refrigerant at a high pressure into the crank chamber, a valve unit arranged in a portion of the fluid supply passage to open and close the portion of the fluid supply passage, a fluid withdrawal passage extending from the crank chamber to the suction chamber to maintain a constant fluid communication between both chambers, and a valve control mechanism to control the opening and closing operation of the valve unit. Namely, the valve control mechanism operates in such a manner that when the pressure in the crank chamber is reduced to below a predetermined reference value, it operates the valve unit to move to its open position where the refrigerant at a high pressure is supplied from the discharge chamber into the crank chamber. Further, when the pressure in the crank chamber goes up beyond the predetermined reference value, the valve control mechanism operates the valve unit to be moved to its closed position where the supply of the refrigerant at a high pressure from the discharge chamber to the crank chamber is stopped. The valve unit and the valve control mechanism constitute an integral displacement control valve unit.
When the compressor is operated under a first condition in which the valve unit of the displacement control valve unit is moved to its closing position to stop the supply of the refrigerant gas at a high pressure from the discharge chamber to the crank chamber, the refrigerant gas leaking from a compression chamber in the cylinder bore into the crank chamber, i.e., a blow-by refrigerant is withdrawn continuously from the crank chamber into the suction chamber via the fluid withdrawal passage. Thus, a reduction in the pressure in the crank chamber occurs. Subsequently, when a temperature in the objective area, i.e., a temperature in a vehicle compartment is lowered while reducing a refrigerating load, a suction pressure of the compressor is reduced. When a reduction in the pressure in the crank chamber is lowered to a level below the predetermined reference value, the valve unit of the displacement control valve unit is moved to its opening position. Therefore, a refrigerant at a high pressure is supplied from the discharge chamber into the crank chamber to increase a pressure in the crank chamber. When the pressure in the crank chamber is increased to go up beyond the predetermined value, the valve unit of the displacement control valve unit is moved to its closing position to close the aforementioned portion of the fluid supply passage. Therefore, the pressure increase in the crank chamber is stopped, and the pressure in the crank chamber is held substantially at the predetermined value during the ordinary operation of the compressor. A difference between the pressure in the crank chamber and the suction pressure of the compressor relying on a change in the refrigerating load of the climate control system adjustably changes the reciprocating stroke of the piston mechanism to thereby control the displacement of the compressor. Although the above-mentioned displacement control valve unit is arranged so as to control the opening and closing operation of the valve unit thereof in response to detection of a change in the pressure prevailing in the crank chamber, the controlling operation of the displacement control valve unit may be carried out in a different manner. For example, the displacement control valve unit may be constructed to operate in such a manner that the movement of the valve unit thereof to its open and closed positions is controlled in response to detection of a change in the suction pressure of the refrigerant compressor. Further, the displacement control valve unit may include a valve unit thereof arranged in a portion of the fluid withdrawal passage in the refrigerant compressor so as to control withdrawing of the refrigerant from the crank chamber into the suction chamber.
It should be noted that the above-mentioned displacement control valve unit is conventionally assembled in either a cylinder block or a rear housing of a variable displacement type refrigerant compressor. FIG. 4 typically illustrates a conventional control valve unit 20 assembled in a rear housing 3. The control valve unit 20 is provided with a suction pressure chamber 21 functioning as a pressure sensing chamber, and a discharge pressure chamber 22 arranged axially opposed to the suction pressure chamber 21 and functioning as a valve chamber. The suction pressure chamber 21 is arranged so as to communicate with the suction chamber 3a of the refrigerant compressor via a passage 23 formed in the rear housing 3, and the discharge pressure chamber 22 is arranged so as to communicate with the discharge chamber 3b of the refrigerant compressor via a passage 24 formed in the rear housing 3. Within the suction pressure chamber 21, a bellows element 26 is centrally arranged so as to axially expand or contract and to define therein an atmospheric chamber 25. A spring 27 is arranged so as to constantly urge the bellows element 26 toward its extended position, i.e., toward the discharge pressure chamber.
The discharge pressure chamber 22 has a valve hole 28 formed at an end thereof confronting the suction pressure chamber 21 so as to communicate with a valve port 29 which is arranged to communicate with the crank chamber 2a of the refrigerant compressor via a fluid supply passage 30. A valve rod 31 connected at its one end to the bellows element 26 extends toward the discharge pressure chamber 22 so that the other end thereof enters into the discharge pressure chamber 22 via the valve port 29 and the valve hole 28.
A valve element 32 is attached to the other end of the above-mentioned valve rod 31 within the discharge pressure chamber 22 so as to oppose to the valve hole 28. The valve element 32 is thus able to open and close the valve hole 28, in response to the expanding and contracting movement of the bellows element 26, and is constantly urged by the spring force of a spring 33 toward the closed position thereof to close the valve hole 28. Therefore, when the suction pressure introduced into the suction pressure chamber 21 goes down below a predetermined set value, the bellows element 26 is expanded to move the valve rod 31 so that the valve element 32 is moved away from the valve hole 28. Namely, the valve hole 28 is opened, and accordingly, the refrigerant gas at a discharge pressure (a high pressure) is supplied from the discharge chamber 3b into the crank chamber 2a via the valve hole 28, the valve port 29 and the fluid supply passage 30.
Nevertheless, the displacement control valve unit 20 is constructed so that the suction pressure chamber 21 in which the suction pressure Ps is introduced via the passage 23 to be sensed by the accommodated movable bellows element 26, the discharge pressure chamber 22 having two holes opening toward the fluid supply passage 30 and the discharge chamber 3b and accommodating therein the valve element 32 to open and close the valve hole 28, and the valve rod 31 transmitting the expanding and contracting movement of the bellows element 26 to the valve element 32 to thereby move the valve element 32, are integrally incorporated in a single member forming a casing member 34 of the displacement control valve unit 20 as shown in FIG. 3 and FIGS. 5A and 5B. Namely, the casing member 34 must be provided as an indispensable element of the displacement control valve unit 20, and the bellows element 26 must be seated on and welded to a seat 37 (37a or 37b) before the bellows element 26 is accommodated in the suction pressure chamber 21 of the casing member 34. Further, the casing member 34 of the valve control unit 20 must be provided with a plurality of grooves to contain therein o-rings 35 in order to fixedly disposed in an assembling bore of the rear housing 3 (or the cylinder block 1) when the control valve unit 20 is assembled in a compressor body. As a result, a large assembling space is needed to accommodate the control valve unit 20 in the body of the refrigerant compressor. In addition, the assembling of the control valve unit 20 requires delicate assembling operation performed by an operator and thus, causes an increase in the manufacturing cost.
Furthermore, since the bellows element 26 functioning as the pressure sensing element is a movable element permitted to expand and contract over a range of only 1 through 2 millimeters, the whole length of the casing member 34, the position to dispose the bellows element 26 within the suction pressure chamber 21, the bore depth in the casing member 34 which forms the suction pressure chamber 21 and the discharge pressure chamber 22 must be formed by machining at a very high accuracy to minimize a cumulative error due to addition of dimensional tolerances of the machined portions of the casing member 34.